198 Studies in Forestry [CHAP. ix. 



to approach each other in an endeavour to form canopy, the 

 clearance has of course 'to be repeated, in order that the 

 foliage on the lower branches, and within the interior of the 

 crowns, may not be hindered in its assimilative functions, 

 owing to the decreased measure of exposure to light and air to 

 which they must be reduced in anything like close canopy. 

 As in regard to thinnings, there can be no hard and fast rules 

 for the conduct of partial clearances ; for so much depends on 

 the quality of the soil and situation. But, practically, they 

 should be repeated at intervals of about five to ten years at 

 first, and about ten to fifteen years later on. Oak woods 

 treated in this manner about the fiftieth to sixtieth year should, 

 according to Gayer 1 , yield a quantitative annual increment of 

 from 3 to 3! % up to their looth year, and 2 to z\ % after that, 

 without taking into consideration the qualitative, technical, 

 and financial increment simultaneously rising more rapidly. At 

 120 years of age the Oak woods treated thus should show about 

 thirty-six to forty-eight stems per acre. Larch crops partially 

 cleared from the thirtieth to thirty-fifth year onwards should, 

 on situations naturally adapted for their growth, at sixty to 

 seventy years of age show about sixty to seventy trees per acre 

 with an annual increment of from 3 to 4 %. In Scots Pine 

 woods a repetition of the process is only advisable on the 

 better classes of soil, as, otherwise, experience has shown that 

 better results can generally be achieved by letting the whole of 

 the standard trees come together to form the light canopy 

 which is their characteristic on inferior soils and situations, 

 and beneath which a crop of underwood can usually thrive fairly 

 well. In mixed woods of Spruce, Silver Fir, and Beech 

 excellent results have been attained by beginning to thin rather 

 heavily about the thirtieth year, repeating the thinnings every 

 tenth year, and then making a partial clearance between the 

 sixtieth to seventieth year, so as to leave per acre- about 120 

 to 1 60 trees of sound, promising growth. In crops thus 

 1 Op. '/., pp. 574, 575- 



